Answer:
Acid, Horizontally, Drain off the acid by opening the stopcock
Step-by-step explanation:
A buret is a calibrated glass appratus used to measure and deliver accurate volume of liquid, usually acids, in acid-base titrations.
Before usually the buret to carry out your titration reaction, it is advised to condition or prepare your buret for use.
To condition the buret, add a small volume of the acid to the buret and rotate the barrel horizontally to ensure that the liquid ( acid) makes contact with the inner surface of the barrel o the buret.
This procedure is done to wash off any previous acid or liquid that the buret had been used for in previous titrations.
Complete this action by opening the stopcock of the buret to drain off the acid and discarding each volume in a designated waste container.
Note that acids could be corrosive and dangerous to the skin and so should be handled with great care